High thermal transfer hollow core extrusion screw assembly

Abstract

High thermal transfer, hollow core extrusion screws (50, 52, 124, 126, 190) include elongated hollow core shafts (54, 128, 130, 192) equipped with helical fighting (56, 132, 134, 194) along the lengths thereof. The fighting (132, 134, 194) may also be of hollow construction which communicates with the hollow core shafts (54, 128, 130, 192). Structure (88, 90) is provided for delivery of heat exchange media (e.g., steam) into the hollow core shafts (54, 128, 130, 192) and the hollow fighting (132, 134, 194). The fighting (56, 132, 134, 194) also includes a forward, reverse pitch section (64, 162, 216). The extrusion screws (50, 52, 124, 126, 190) are designed to be used as complemental pairs as a part of twin screw processing devices (20), and are designed to impart high levels of thermal energy into materials being processed in the devices (20), without adding additional moisture.

We claim: 
     
       1. A twin screw processing device operable to create a food product from a mixture of food ingredients, said device comprising:
 an elongated barrel having a material inlet for said mixture and a processed material outlet comprising a transfer pipe secured to said barrel outlet, and a restricted orifice die operably coupled with said transfer pipe; 
 a pair of elongated, axially rotatable, helical screws within said barrel, each of said screws having an elongated shaft with a hollow core, and elongated helical fighting extending outwardly from said shaft, said elongated shaft hollow core configured to receive heat exchange media, 
 said helical screws configured for driven, directional co-rotation at a rotational speed of from about 30-150 rpm; and 
 a media delivery assembly including a pair of media delivery tubes extending from a point outside of said barrel and respectively into a corresponding one of said elongated shaft hollow cores, and structure coupled with said delivery tubes permitting introduction of media to said tubes for delivery into said elongated shaft hollow cores, 
 each of said helical screws having a first helical fighting section with a pitch length D 1  of from about 0.4-1.2 based upon the diameter of the first helical fighting section and operable to convey material from said material inlet toward and through said processed material outlet, and a second helical flighting section proximal to said processed material outlet and operable to retard the flow of material therepast, said first and second helical fighting sections being of opposite hand, said second helical fighting section being shorter than said first helical fighting section and having a pitch length smaller than the pitch length of said first helical flighting section, 
 said first and second helical flighting sections being intermeshed along the lengths thereof, and 
 at least a portion of said first helical fighting section having a hollow helical area along the length of said first helical fighting section portion, said helical area being open along at least a part of the length thereof, said helical area being in communication with said hollow internal region and said elongated shaft hollow core, 
 said intermeshed, co-rotating helical screws, said pitch lengths D 1 , and the rotational speeds of said helical screws, selected to increase shear conditions within said barrel, to generate a temperature of at least about 90° C., and to create a pressure level within the barrel of from about 200-600 psi, during processing of said mixture. 
 
     
     
       2. The processing device of  claim 1 , said structure comprising a pair of rotary unions respectively and operably secured to a corresponding delivery tube. 
     
     
       3. The processing device of  claim 1 , said portion of said fighting section having a pair of opposed, spaced apart wall segments extending outwardly from said shaft with a hollow helical area between the opposed wall segments, said wall segments having a helical transition area between the opposed wall segments, said transition area being open throughout the length and width thereof to afford unobstructed communication between said screw section hollow internal region and said elongated shaft hollow core. 
     
     
       4. The processing device of  claim 3 , said transition area including an inner wall with a series of spaced apart apertures through said inner wall communicating said helical groove with said elongated shaft hollow core. 
     
     
       5. The processing device of  claim 1 , the thickness of said shaft being substantially equal to the thickness of said helical fighting section. 
     
     
       6. The processing device of  claim 1 , said first screw section being of unitary, cast construction. 
     
     
       7. The processing device of  claim 1 , each of said media delivery tubes extending substantially the full length of said fighting sections. 
     
     
       8. The processing device of  claim 1 , the flight depths of said first helical flighting section and said second helical flighting section being substantially equal. 
     
     
       9. The processing device of  claim 1 , said pitch lengths D 1  being from about 0.5-1.0.